Means for preventing destructive field-magnet discharges



(No Model.)-

P. MAGKINTOSH. MEANS FOR PREVENTING DESTRUGTIVE FIELD MAGNET DISGHARGES.

No. 5711 11. Patented Feb. 16,1897.

UNITED STATES PATENT OFFICE.

FREDERICK MACKINTOSI-I, OF SCHENECTADY, NEIV YORK, ASSIGNCR TO THE GENERAL ELECTRIC COMPANY, OF NEIV YORK.

MEANS FOR PREVENTING DESTRUCTIVE FIELD-MAGNET DISCHARGES.

SPECIFICATION forming part of Letters Patent No. 577,141, dated February 16, 1897.

Application filed October 31,1896. Serial No. 610,676. (No model.)

1'0 all whom it may concern:

Be it known that I, FREDERICK MAOKIN- TOSH, a citizen of the United States, residing at Schenectady, in the county of Schenectady, State of New York, have invented cer tain new and useful Improvements in Means for Preventing Destructive Field-Magnet Discharges, (Case No. 418,) of which the following is a specification.

\Vhen dynamo-electric machines are shut down and the field-circuit interrupted, an electromotive force is induced in the coils of the field-winding by the dying out of the magnetism,the voltage of which is often many times greater than that of the exciting-current. This is extremely liable to destroy the insulation of the field-spools.

In machines of large size having many poles the kick, as it is called, is often very great, which renders it necessary to provide some means-as an incandescent lamp, for exampleto consume the energy thus produced. This method has proven in actual practice to be very unsatisfactory. As many as eighteen lamps in series have been blown in pieces by the discharge from a machine of this type, which, as will readily be seen, is unsatisfactory and expensive.

The present invention has for its object to provide means for preventing the destructive discharge from the field-magnet coils.

In carrying out the invention a source of electromotive force is provided of such a character that when connected across the terminals of the field-circuit and the exciting-circuit interrupted it sends a current through the field-coils in the same direction and at a potential. approximately equal to that of the exciting current, but which gradually decreases to zero, permitting the field to die out in a natural manner without any destructive kick.

In the accompanying drawing, attached to and made part of this specification, A A are alternating-current generators provided with a number of fieldmagnet coils receiving their energizing-current from the bus-bars a a, supplied by means of the direct-current exciter B. WVhile only two alternators are shown, it is to be understood that the invention contemplates using any number of generators and supplying their exciting-current from one or more exciter-dynamos.

In circuit with the field-coils D of each machine is an adjustable rheostat R, adapted to vary the field excitation of the dynamos for regulating their output. The armatures E are connected in multiple with the bus-bars I F, from which feeders extend to the external or work circuit. Each field-circuit is provided with a double-pole switch G, and ex tending therefrom are leads to the switches G. The latter are to close the circuit between the supplementary bus-barsI I and the field-circuit.

C is an auxiliary machine having its fieldcoil supplied with current from the exciter B by means of leads extending from the busbars a a. Included in these leads is a doublepole switch J for interrupting the circuit when the auxiliary machine C is not in use. The armature C is permanently connected through a resistance 0, which may be variable, with the bus-bars L L. On the shaft of the armature C may be mounted a flywheel C (shown in dotted lines) for preventing the too sudden slowing down of the ar mature after a load is thrown thereon.

Assuming that it is desirable to shutdown the machine A, the switch J is closed for the purpose of supplying exciting-current to the field-magnets of machine C. The switch G is then closed, which includes the armature C in multiple circuit with the field D of the machine A. After the armature C obtains its maximum speed the switch G is opened, disconnecting the field-coils D from the exciter 13. The armature C now revolving by its momentum in a magnetic field produces a current which flows through the field-coils D in the same direction as that of the exciting-current and at a potential substantially equal thereto. As the speed and current of the armature C are reduced, the field-mag netism dies out slowly, prevent-ing any sudden discharge of the field-coils.

Assuming that the potential of the main excited current is one hundred volts, there is a counter electromotive force generated in the armature C amounting, for example, to

ninety-live volts, which, as soon as the exciting-eireuit is interrupted, sends a current through the field-coils D, maintaining the same direction of magnetization as the main exciting-current. The difference in voltage between the exciting-circuit and the Voltage of the armature 0 being so slight, no spark is occasioned when the switch G is opened.

It is within the spirit of my invention to employ a storage battery or other similar apparatus in place of the machine 0, the essential feature being to provide an eleetromotive force acting to pass current through the lieldcoils D in the same direction as that of the main exeiter, with means for grad uall y red ucing the eleetromotive force to zero.

An advantage to be derived from the present invention is that higher exciting-potentials may be employed, with the consequent economy in field-winding and regulators.

What I claim as new, and desire to secure by Letters Patent 01' the United States, is

1. The art of preventing destructive discharge from field-magnet coils, which consists in including in circuit with the fieldanagnet coils and the exciter a secondary source of electromotive force, interrupting the circuit of the excltcr causing the secondary source of electromotive force to energize the fieldeoils, and decreasing the secondary electro motive force.

2. As a means of preventing destructive discharge from field-magnet coils, the combination of an exciter supplying current to the field-magnet, a source of secondary clectromotive force in circuit with the exciter, means for interrupting the eXciter-circuit causing the secondary source of GlOChlOll'lOlllVQ force to energize the held-col ls, and means for de creasing the secondary electromotive force.

3. As a means for preventing destructive discharge from field-magnet coils, the combination of an exciter supplying current to the field-coils, a dynamo-electric machine in circuit therewith, and a switch fol-interrupting the eXeiter-circuit and causing the motor to act as a generator and supply current to the field-coils.

l. As a means for preventing destructive discharge from field-magnet coils, the combi nation of an exciter supplying current to the field-coils, a motor having its armature included in circuit with the field-coils to be dis charged, field-coils for the motor excited from a suit-able source of energy, and a switch for interru 'lting the eXciter-eircuit and. causing the 1notor-arnnitture to supply current to the field-coils in circuit therewith.

5. In combination, a plurality of dynamo electricmachines receivingthcirexciting-eurrent from a common source, a motor having its field magnets excited from asouree elf con stant potential, switches for including the armature of themotorin the lield-cimuil of any of the dynamo-electric machincsnnd a switch for interrupting the exciting-circuit elf the machine to which the armature is con nee ted, and causing the armature to supply current to the field-eoils of the machine.

In witness whereof I have hereunto set my hand this 23d day of October, 18%.

FREDERICK MACKINTUSII.

\Vitnesses:

l B. HULL, E. \V. CADY. 

